In circuit-breakers of this type, two arcing contact pieces, located coaxially opposite each other, are coaxially surrounded by the two continuous-current contact pieces, of which one is arranged in a fixed position and the other one is axially driveable. Circuit-breakers of this type generally operate with a gaseous quenching medium which, in a switching operation, is first compressed and then flows through the separation area of the two arcing contact pieces, it being possible to influence its flow by special pressure spaces and nozzles. Used for this purpose, inter alia, is an insulating nozzle which is arranged inside the continuous-current contact pieces and surrounds the arcing contact pieces, and which is firmly connected both to the driveable continuous-current contact piece and to the driven arcing contact piece.
In a known circuit-breaker described in, for example, (European No. 0 696 040), a field electrode, which is secured to the end of the insulating nozzle facing away from the first driven arcing contact piece and can be axially displaced together with the insulating nozzle, surrounds the second arcing contact piece and, when the circuit-breaker is in the OFF position, influences the electric field in the area of the other arcing contact piece and of the electrically heavy-loaded end of the insulating nozzle. In addition, in this circuit-breaker, the second arcing contact piece can be driven in the opposite direction of the first arcing contact piece. To this end, a driving element is secured to the axially displaceable field electrode, and thus to the insulating nozzle, the driving element transferring the driving motion of the driven continuous-current contact piece to the second arcing contact piece as well, using a deflection (corner) gear. Therefore, the second arcing contact piece is guided in a sliding contact. The driving element in the deflection gear is designed as a gear rack which either acts via a gear wheel upon the second arcing contact piece, also designed as a gear rack, or which drives a thrust crank whose rotating part is formed by a gear wheel.
In this circuit-breaker, the field electrode secured to the insulating nozzle follows the full stroke (travel) of the contact pieces; that means that in the ON position, the field electrode is inserted relatively far into the fixed continuous-current contact piece, requiring a corresponding space. The movement of the second arcing contact piece is also linked to the full stroke of the driven contact pieces.